This invention relates to antenna systems, and more particularly to antenna systems that in operation are enclosed in a radome that is mounted on an aircraft. Typically, in such systems the radome is mounted either on top of or underneath the aircraft; and the antenna system that is enclosed therein is rotated 360.degree. in the horizontal plane to scan the horizon in all directions.
One problem encountered with the design of such systems is that of simultaneously meeting the conflicting requirements of a broad frequency band, a high gain, and a low drag on the aircraft. Basically, to increase the frequency band of an antenna array, the number of radiating elements must by increased. Thus, more space is required in the radome for these elements. The problem is most severe when the frequency range to be extended is at the low end of the band. This is because the size of a radiating element is roughly inversely proportional to the frequency being radiated.
Similarly, to improve the gain of an antenna array, a parabolic reflector may be used. In general, the gain increases as the size of the reflector is increased. However, a large reflector necessitates the use of a large radome, which in turn increases the drag on the airplane.
The drag caused by a radome is roughly proportional to the square of its cross-sectional area. Thus, it is highly desirable to minimize the radome's size.
Therefore, it is one object of the invention to provide an improved compact high-gain broadband antenna system for use within a radome of predetermined size.